1. Field of the Invention
This invention relates generally to printing apparatus and, more particularly, to a color video printer in which light is projected onto a color sensitive printing paper, such as an instant and self-developing photo-sensitive film, through a liquid crystal shutter that is controlled by a video signal.
2. Description of the Background
A printing apparatus that can obtain a so-called hard copy of a visual image corresponding to a video signal recorded by an electronic still camera or to a video signal supplied from a television receiver is described in Japanese Pat. Laid-Open Gazette No. 60-81986. That Japanese published application describes a printing apparatus in which a color image corresponding to a video signal can be formed by irradiating light onto a color sensitive printing paper through liquid crystal shutters whose opening and closing is controlled by the video signal. This kind of printing apparatus utilizing liquid crystal shutters is low-powered and compact-sized and is inexpensive, so that it is now becoming commercially viable as a home color video printer.
When a color visual image is projected onto a color sensitive printing paper by the prior-art printing apparatus utilizing liquid crystal shutters, as shown in FIG. 1, a color picture element 1, which is the minimum unit of the color image and may be thought of as one colored dot. This color picture element 1 is formed of a red portion 2R of a red micro-shutter element, a green portion 2G of a green micro-shutter element, and a blue portion 2B a blue micro-shutter element. In FIG. 1, a separating band portion 3 of the color picture element 1 separates the respective micro-shutter elements.
Using the known liquid crystal shutter, if the magnification of optical system is taken as "1", the area of the picture dot resulting from color picture element 1 can only be the sum of the areas of the three micro-shutter elements 2R, 2G, 2B in the liquid crystal shutter, so that resolution of the color visual image is limited.